1. Field of the Invention
The present invention relates to an electrically conductive adhesive in an electric circuit board. The adhesive, which is basically made from the heat-curable silicone resin, shows excellent adhesiveness to an inorganic substrate and excellent thermal conductivity. The conductive adhesive is useful as an electronic component.
2. Technical Background
Solder provided with both electrical conductivity and adhesiveness has been conventionally used to adhere electronic components to a substrate or electric circuit when mounting on an electric circuit board. In recent years, however, there has been a tendency to avoid the use of solder containing lead. Also, the detrimental effect of heat possessed by molten solder on electronic components that lack heat resistance may also become a problem. Therefore, electrically conductive adhesives consisting mainly of a resin and a metal powder have come to be used in recent years. The advantages of these electrically conductive adhesives consist of being lead-free, having a lower treatment temperature than solder, and having a low specific gravity that contributes to reduced weight of electronic equipment. Various attempts have been made to improve the adhesiveness of electrically conductive adhesives containing resin as a main ingredient.
US2001-015424 discloses an electrically conductive adhesive that adheres two electrodes. According to this document, adhesive strength of the electrically conductive adhesive is improved by being composed of a resin having a functional group that forms a coordinate bond with the metal of the electrodes. This solves the problem of separation of the electrodes and the electrically conductive adhesive that frequently occurs in electronic components having large surface areas that are susceptible to bending stress.
US2005-288427 describes an anisotropic electrically conductive adhesive composed of an insulating resin containing a crosslinkable rubber-like resin and electrically conductive particles. According to US2005-288427, separation of the electrically conductive adhesive is prevented, where the rubber-like resin minimizes thermal shrinkage of the anisotropic electrically conductive adhesive that occurs during a polymerization or curing reaction during heating and adhesion. In addition, a silane coupling agent is added to improve the adhesion environment of adhesive surfaces.
However, electrically conductive adhesives composed of conventional thermoplastic organic binder resins still lack adhesiveness to many inorganic substrates or electrodes. In addition, since electric components or electric devices mounted on a substrate with an electrically conductive adhesive have low heat resistance, there is the problem of deterioration of these components or devices in the process during which the adhesive is heat-cured. In addition, where there is increasing amounts of heat generated from electronic components in the manner of IC chips and LED chips, accompanying the higher levels of performance and reduced size of electronic components, it is difficult to dissipate this heat. Moreover, in the case where the electronic device is a light source, organic adhesives may be deteriorated by ultraviolet light.
The present invention addresses the problems of improving adhesive strength and heat releasability during mounting of components with an electrically conductive adhesive.